Chemical changes occurring during the storage of black tea

The deterioration of black tea, characterised by a loss of flavour and astringency and sometimes by the acquisition of undesirable “taints” is accompanied by lipid hydrolysis and by autoxidative reactions that cause losses of theaflavins, amino acids, sugars, photosynthetic pigments and some volatile aliphatic constituents and increases in non‐dialysable pigments and some volatile phenolic components. These reactions are accelerated by moisture and heat. Although lipid oxidation is insignificant except under hot dry conditions, it is postulated that oxidation of free fatty acids released during storage occurs during brewing, and has a profound influence on the quality of the liquor.